International Research Journal of Insect Sciences 2014 Vol.1, No.1, pp.1-11 ISSN(e): 2408-9281 ISSN(p): 2412-3439 © 2014 Conscientia Beam. All Rights Reserved. OLFACTORY RESPONSE OF AN ASSASSIN BUG, RHYNOCORIS LONGIFRONS (INSECTA: HEMIPTERA: REDUVIIDAE) TO THE HEXANE EXTRACTS OF DIFFERENT AGRICULTURAL INSECT PESTS A. Ganesh Kumar1 --- Dunston P. Ambrose2 1,2Entomology Research Unit, St. Xavier’s College (Autonomous), Palayamkottai, Tamil Nadu, India ABSTRACT The predator-prey interaction of five prey species with the assassin bug, Rhynocoris longifrons (Stål) (Hemiptera: Reduviidae) was assessed in a Y-shaped olfactometer and the prey preference was assessed in six-arm olfactometer provided with the bodyextracts in hexane. Although R. longifrons responded to all the hexane extracts of testedinsect pests, R. longifrons showed maximum response to the lepidopterans Spodoptera litura (F.) (6.67±1.18 min), Helicoverpa armigera (Hübner) (5.17±0.89 min) and Achaea janata (L.) (4.42±1.04 min) followed by the coleopteran Mylabris indica (Thunberg) (3.00±0.82 min) and the least response to the hemipteran Dysdercus cingulatus (F.) (2.42±0.76 min).Thus, the present study clearly reveals the order of the host preference of R. longifrons to the tested hexane extracts of the taxonomically diverse insect pests. Keywords: Assassin bug, Rhynocoris longifrons, Kairomonal ecology, Olfactometer, Spodoptera litura, Helicoverpa armigera, Achaea janata, Mylabris indica, Dysdercus cingulatus. Contribution/ Originality This paper contributes the first hand information on the allelochemical interaction of Rhynocoris longifrons with its prey species Spodoptera litura, Helicoverpa armigera, Achea janata, Dysdercus cingulatus and Mylabris indica and reveals its prey preference. It also enables one to employ R. longifrons as a biocontrol agent against these insect pests. 1. INTRODUCTION The Reduviidae is the largest family of predaceous land Hemiptera and many of its members are found to be potential predators of a number of insect pests [1]. Since they are polyphagous they may not be effective on specific pests, but they are valuable predators in situations where a variety of insect pests occur. Rhynocoris longifrons (Stål) (Hemiptera: Reduviidae) is an harpactorine assassin bug predating upon insect pests such as cotton bollworm Helicoverpa 12 © 2014 Conscientia Beam. All Rights Reserved. International Research Journal of Insect Sciences, 2014, 1(1): 12-19 armigera (Hübner), plume moth Exelastis atomosa Walsingham, tur pod bug Clavigralla gibbosa Spinola, green stink bug Nezara viridula (Linnaeus) andpod bug Riptortus pedestris (Fabricius) [2]. Chemical and/or physical cues from the host, the substrate and associated material and/or organisms play a fundamental role in mediating the different steps of host selection [3-5]. Volatiles are important cues for many arthropods. Use of chemicals emanating from the host and its by-products which enhance the behavioural dynamics of entomophages increasing their effectiveness were advocated [6-8]. Semiochemicals help natural enemies to locate and recognize their hosts or prey [9, 10] and elicit behavioural and physiological responses in the receiver, which results in the interaction between them [11]. Behavioural chemicals that provide cues for orientation of predators in the prey finding sequence includes secondary plant metabolites and chemicals directly associated with the host prey [12]. Antennectomy studies by various authors on the predatory behaviour of reduviids revealed that, these predators use the prey chemical cues to locate their prey[13][14], [15]. Thus, it seemed likely that the reduviids utilize chemicals released by their prey as kairomone in prey location. Only few studies have been undertaken on the allelochemical relationship between reduviids and their prey location behaviour. Mere augmenting and releasing the biocontrol agents into the agroecosystems will not be successful unless the behavioural dynamics of reduviid predators to chemical cues of the prey is known. Hence, the behavioural responses of R. longifrons to the solvent extracts of tobacco leaf armyworm Spodoptera litura (Fabricius), H. armigera, castor semilooper Achea janata (Linnaeus), red cotton bug Dysdercus cingulatus (Fabricius) and blister beetle Mylabris indica Thunberg were investigated since these are major insect pest of cotton, in order to understand the prey preference and prey-location behaviour of the predator using kairomonal cues, if any, that elicit from prey belonging to diverse orders. 2. MATERIALS AND METHODS 2.1. Predator Collection and Maintenance The adults of R. longifrons were collected from Muppandal Scrub Jungle (77°31' E and 8°22' N), Tamil Nadu, South India and were reared in the laboratory under optimal conditions (temperature 30 ± 1º C; RH 75 ± 5 %; Photoperiod 12 ± 1 hr.) in plastic containers on the larvae of Corcyra cephalonica Stainton ad libitum. 2.2. Pest Collection and Maintenance Lepidopteran insect pests viz., S. litura, H. armigera and A. janata and a hemipteran pest D. cingulatus and a coleopteran pest M. indica were used in this study as these are economically important and collected from cotton, lady’sfinger and castor agroecosystems in and around Palayamkottai (77°73'E and 8°72'N), Alankulam (77o54'E and 8o93'N) and Pavoorchatram (77o55'E and 8o10'N) agroecosystems. The H. armigera larvae were maintained on fresh lady’sfinger fruits, cotton bolls and flowers in plastic containers (7 x 7 cm) separate. The S. litura and A. janata larvae were maintained on fresh cotton and castor leaves in the plastic troughs (15 x 13 © 2014 Conscientia Beam. All Rights Reserved. International Research Journal of Insect Sciences, 2014, 1(1): 12-19 30 cm). The adults of M. indica were maintained on fresh lady’sfinger and cotton flowers in a mesh cage (5 x 2x 3 ft). The adults of D. cingulatus were maintained on wet cotton seeds in a mesh cage (5 x 2x 3 ft). 2.3. Solvent Extracts of Prey Species The whole body extracts of different prey species were prepared following the methodology of Yasuda [16]. Hundredlive fifth instars lepidopteran larvae of S. litura, H. armigeraand A. janataand adults of coleopteran M. indica and hemipteranD. cingulatus, were kept in reagent bottles having 1:2 mixtures of hexane and acetone for 30 minutes at room temperatures, separately and subsequently stored in a freezer overnight. The solvent extracts were then filtered through a Whatman No.1 filter paper. Thereafter, the filtered solvent extracts were evaporated in a vacuum desiccator under room temperature and the residues were dissolved in 100 ml of ether, separately. Then the ether was washed off with 50 ml of distilled water thrice. Thereafter, the ether-soluble layer was dried over sodium sulfate. Then the solvent was removed by using vacuum desiccator at room temperature and the residue was dissolved in hexane. The resultant extracts were stored at below -20o C until further use. 2.4. Behavioral Bioassay A Y-shaped olfactometer made up of glass (main stem 20 cm length, two arms 15 cm length and 5 cm diameter, each and 90o between them.) was used for the bioassay studies i.e., to test the predator response to individual extracts. The two arms were connected to 6.5 cm diameter glass chambers (odour cells), in which the prey solvent extracts (odour sources) could be placed. Before starting the experiment the Y-shaped olfactometer with odour cells were cleaned with 70 % alcohol followed by continuous blowing of air by an aerator for 15 minutes to remove the unwanted odour from the odour cells. The air was blown into the two arms of the olfactometer using a small ‘T’ tube and the air was allowed to pass outside through the exit tubes of odour cells. A small piece of sterile cotton impregnated with body extract of insect pests (100 µl of a sample) was used as test and cotton impregnated with hexane was used as control (100 µl of hexane). The 24hr starved predators were introduced through the main stem and their predatory behaviour was observed for 30 mins continuously. The predatory behaviour was observed in terms of approaching and sucking time. From these observations, the handling time was calculated by summing up both [17]. The predators choose either the test chamber with body extract or the control chamber with hexane or neither. Predator chooses the test chamber or control chamber considered as positive choice or negative choice, respectively. If the predator chooses neither of the chambers, then it was considered as no choice. The experiment was replicated 12 times with 24 hour starved and inexperienced predators on each body extract of insect pests, separately with new impregnated cotton for each replicate. 14 © 2014 Conscientia Beam. All Rights Reserved. International Research Journal of Insect Sciences, 2014, 1(1): 12-19 The approaching time taken by the predators in the olfactometers to different body extracts was converted into an index called Excess Proportion Index (EPI) [18] using the following formula: EPI= (NS-NC)/ (NS+NC) Where, NS- Number of predators choosing the sample cell. NC- Number of predators choosing the control cells EPI values are ranging from +1 to -1. These terms simply express polarity of the directional choice. Positive values indicate a positive approach response. The assay for contact chemicals consist of counting antennation and probing frequencies towards each test sample, at given period of time. 2.5. Six-Arm Olfactometer The six arm (each arm 20cm long) olfactometerwas used to compare predator attraction to all five extracts, made up of glass had six arms, each arm terminating with an odour cell. The arms met at a central cell. At a time five odour cells can be used as test cells, each with one prey extract (20µl) impregnated in sterile cotton and the sixth cell as control cell with hexane alone (20µl) impregnated in sterile cotton. Before the introduction of predators, air was blown with aerator into the central cell and from there to the arms and odour cells to remove the odour, if any in the olfactometer.